---
title: Writing agent state
icon: "lucide/ArrowRight"
description: Write to agent's state from your application.
---
import RunAndConnect from "@/snippets/integrations/pydantic-ai/run-and-connect.mdx"
import { IframeSwitcher } from "@/components/content"

<IframeSwitcher
  id="shared-state-write-example"
  exampleUrl="https://feature-viewer.copilotkit.ai/pydantic-ai/feature/shared_state?sidebar=false&chatDefaultOpen=false"
  codeUrl="https://feature-viewer.copilotkit.ai/pydantic-ai/feature/shared_state?view=code&sidebar=false&codeLayout=tabs"
  exampleLabel="Demo"
  codeLabel="Code"
  height="700px"
/>

<Callout type="info">
  This example demonstrates writing to shared state in the [CopilotKit Feature Viewer](https://feature-viewer.copilotkit.ai/pydantic-ai/feature/shared_state).
</Callout>

## What is this?

This guide shows you how to write to your agent's state from your application.

## When should I use this?

You can use this when you want to provide the user with feedback about what your agent is doing, specifically
when your agent is calling tools. CopilotKit allows you to fully customize how these tools are rendered in the chat.

## Implementation

<Steps>
  <Step>
    ### Run and connect your agent
    <RunAndConnect components={props.components} />
  </Step>
  <Step>
    ### Define the Agent State

    Create your Pydantic AI agent with a stateful structure. Here's a complete example that tracks language:

    ```python title="agent.py"
    from textwrap import dedent

    from pydantic import BaseModel
    from pydantic_ai import Agent, RunContext
    from pydantic_ai.ag_ui import StateDeps


    class AgentState(BaseModel):
        """State for the agent."""
        language: str = "english"


    agent = Agent("openai:gpt-4o-mini", deps_type=StateDeps[AgentState])


    @agent.instructions()
    async def language_instructions(ctx: RunContext[StateDeps[AgentState]]) -> str:
        """Instructions for the language tracking agent.

        Args:
            ctx: The run context containing language state information.

        Returns:
            Instructions string for the language tracking agent.
        """
        return dedent(
            f"""
            You are a helpful assistant for tracking the language.

            IMPORTANT:
            - ALWAYS use the lower case for the language
            - ALWAYS response in the current language: {ctx.deps.state.language}
            """
        )


    app = agent.to_ag_ui(deps=StateDeps(AgentState()))

    if __name__ == "__main__":
        import uvicorn
        uvicorn.run(app, host="0.0.0.0", port=8000)
    ```

  </Step>
  <Step>
    ### Call `setState` function from the `useCoAgent` hook
    `useCoAgent` returns a `setState` function that you can use to update the agent state. Calling this
    will update the agent state and trigger a rerender of anything that depends on the agent state.

    ```tsx title="ui/app/page.tsx"
    import { useCoAgent } from "@copilotkit/react-core"; // [!code highlight]

    // Define the agent state type, should match the actual state of your agent
    type AgentState = {
      language: "english" | "spanish";
    }

    // Example usage in a pseudo React component
    function YourMainContent() {
      const { state, setState } = useCoAgent<AgentState>({ // [!code highlight]
        name: "my_agent", // MUST match the agent name in CopilotRuntime
        initialState: { language: "english" }  // optionally provide an initial state
      });

      // ...

      const toggleLanguage = () => {
        setState({ language: state.language === "english" ? "spanish" : "english" }); // [!code highlight]
      };

      // ...

      return (
        // style excluded for brevity
        <div>
          <h1>Your main content</h1>
          {/* [!code highlight:2] */}
          <p>Language: {state.language}</p>
          <button onClick={toggleLanguage}>Toggle Language</button>
        </div>
      );
    }
    ```

    <Callout type="warn" title="Important">
      The `name` parameter must exactly match the agent name you defined in your CopilotRuntime configuration (e.g., `my_agent` from the quickstart).
    </Callout>

  </Step>
  <Step>
    ### Give it a try!
    You can now use the `setState` function to update the agent state and `state` to read it. Try toggling the language button
    and talking to your agent. You'll see the language change to match the agent's state.
  </Step>
</Steps>

## Advanced Usage

### Re-run the agent with a hint about what's changed

The new agent state will be used next time the agent runs.
If you want to re-run it manually, use the `run` argument on the `useCoAgent` hook.

The agent will be re-run, and it will get not only the latest updated state, but also a **hint** that can depend on the data delta between the previous and the current state.

```tsx title="ui/app/page.tsx"
import { useCoAgent } from "@copilotkit/react-core";
import { TextMessage, MessageRole } from "@copilotkit/runtime-client-gql";  // [!code highlight]

// ...

function YourMainContent() {
  // [!code word:run:1]
  const { state, setState, run } = useCoAgent<AgentState>({
    name: "my_agent", // MUST match the agent name in CopilotRuntime
    initialState: { language: "english" }  // optionally provide an initial state
  });

  // setup to be called when some event in the app occurs
  const toggleLanguage = () => {
    const newLanguage = state.language === "english" ? "spanish" : "english";
    setState({ language: newLanguage });

    // re-run the agent and provide a hint about what's changed
    // [!code highlight:6]
    run(({ previousState, currentState }) => {
      return new TextMessage({
        role: MessageRole.User,
        content: `the language has been updated to ${currentState.language}`,
      });
    });
  };

  return (
    // ...
  );
}
```

### Intermediately Stream and Render Agent State

By default, the Pydantic AI Agent state will only update _between_ Pydantic AI Agent node transitions --
which means state updates will be discontinuous and delayed.

{/* You likely want to render the agent state as it updates **continuously.**

See **[emit intermediate state](/pydantic-ai/shared-state/predictive-state-updates).**  */}
